Scientists say they have identified a gene which may increase the risk of developing autism.

The gene is involved in the production of ATP, a molecule that provides the energy cells need to function.

Researchers in the United States said the risk only applied to people with a certain genetic make-up.

Writing in the American Journal of Psychiatry, they said as many as 10 different genes might be involved in the development of autism.

Autism affects about one in every 1,000 people. It is a developmental disability that affects the way a person communicates and interacts with other people.

People with autism can have problems relating to other people and to the world at large. They can have problems understanding people's feelings or making friends.

Having one of these variants appears to approximately double an individuals risk for the disorder

Dr Joseph Buxbaum

There is growing evidence that the condition may be inherited. Studies suggest parents with one child with autism are 100 times more likely to have another child with the condition compared with other families.

However, scientists agree that the condition is complex and that more than one gene is involved.

Gene tests

Dr Joseph Buxbaum and colleagues at Mount Sinai School of Medicine in New York carried out genetic tests on 411 families, who have members with autism.

They found that they all had variations in the SLC25A12 gene, which is involved in the production of ATP.

The researchers suggested this flaw could disrupt the production of the fuel cells need. They said even minor disruptions could affect the ability of cells to function properly.

However, the researchers said the genetic variations they identified in this study appeared to be quite common.

By themselves, they do not cause autism. They said people with autism probably had this and other genetic mutations.

"Having one of these variants appears to approximately double an individuals risk for the disorder, but it is an accumulation of genetic factors that cause the disease," Dr Buxbaum said. "Our current challenge is to identify more of these genes."

He added: "Identifying all or most of the genes involved will lead to new diagnostic tools and new approaches to treatment."

The National Autistic Society in the UK welcomed the study.

"Scientists over the world are engaged in looking for the genetic roots of autism," a spokeswoman said.

"Some are looking at other chromosomes as loci for possible genes. The NAS welcomes any research which furthers our understanding of the cause and possible treatment of autism."